JP3622650B2 - Optical disk device - Google Patents

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JP3622650B2
JP3622650B2 JP2000259569A JP2000259569A JP3622650B2 JP 3622650 B2 JP3622650 B2 JP 3622650B2 JP 2000259569 A JP2000259569 A JP 2000259569A JP 2000259569 A JP2000259569 A JP 2000259569A JP 3622650 B2 JP3622650 B2 JP 3622650B2
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signal
amplifiers
amplifier
offset voltage
gain
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JP2002074692A (en
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紀一 高坂
著明 真下
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Teac Corp
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Teac Corp
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Priority to CNB011308443A priority patent/CN1155952C/en
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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/12—Heads, e.g. forming of the optical beam spot or modulation of the optical beam
    • G11B7/125—Optical beam sources therefor, e.g. laser control circuitry specially adapted for optical storage devices; Modulators, e.g. means for controlling the size or intensity of optical spots or optical traces
    • G11B7/126—Circuits, methods or arrangements for laser control or stabilisation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/094—Methods and circuits for servo offset compensation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0941—Methods and circuits for servo gain or phase compensation during operation
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0943—Methods and circuits for performing mathematical operations on individual detector segment outputs
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/004—Recording, reproducing or erasing methods; Read, write or erase circuits therefor
    • G11B7/0055—Erasing
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0901—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for track following only
    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11B—INFORMATION STORAGE BASED ON RELATIVE MOVEMENT BETWEEN RECORD CARRIER AND TRANSDUCER
    • G11B7/00—Recording or reproducing by optical means, e.g. recording using a thermal beam of optical radiation by modifying optical properties or the physical structure, reproducing using an optical beam at lower power by sensing optical properties; Record carriers therefor
    • G11B7/08—Disposition or mounting of heads or light sources relatively to record carriers
    • G11B7/09—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following
    • G11B7/0908—Disposition or mounting of heads or light sources relatively to record carriers with provision for moving the light beam or focus plane for the purpose of maintaining alignment of the light beam relative to the record carrier during transducing operation, e.g. to compensate for surface irregularities of the latter or for track following for focusing only

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  • Optics & Photonics (AREA)
  • Mathematical Physics (AREA)
  • Optical Recording Or Reproduction (AREA)

Description

【０００１】
【発明の属する技術分野】
本発明は光ディスク装置に関し、特に、書き換え可能型光ディスクにデータ記録を行う光ディスク装置に関する。
【０００２】
【従来の技術】
記録型光ディスクには、追記型（Ｗｒｉｔｅ Ｏｎｃｅ）と書き換え可能型（Ｅｒａｓａｂｌｅ）とがある。追記型光ディスクであるＣＤ−Ｒ（Ｃｏｍｐａｃｔ Ｄｉｓｋ Ｒｅｃｏｒｄａｂｌｅ）や、書き換え可能型光ディスクであるＣＤ−ＲＷ（Ｃｏｍｐａｃｔ Ｄｉｓｋ Ｒｅｗｒｉｔａｂｌｅ）またはＤＶＤ−ＲＷ（Ｄｉｇｉｔａｌ Ｖｅｒｓａｔｉｌｅ Ｄｉｓｋ Ｒｅｗｒｉｔａｂｌｅ）にはガイド用のプリグルーブ（溝）が設けられている。プリグルーブは例えば中心周波数２２．０５ｋＨｚで極僅かにラジアル方向にウォブル（蛇行）しており、ＡＴＩＰ（Ａｂｓｏｌｕｔｅ ＴｉｍｅＩｎ Ｐｒｅｇｒｏｏｖｅ）と呼ばれる記録時のアドレス情報が、最大偏位±１ｋＨｚでＦＳＫ変調により多重されて記録されている。
【０００３】
このような記録型光ディスクの記録再生を行う光ディスク装置のトラッキング及びフォーカスサーボ回路は、光ビームを光ディスクに照射して光ディスクからの反射光を複数の光検出器で検出し、この検出信号を用いて所定の演算をすることによりサーボ信号を生成し、これに基づいてアクチュエータを駆動してトラッキング及びフォーカスサーボを行っている。
【０００４】
ここで、書き換え可能型光ディスクであるＣＤ−ＲＷ等の記録再生を行う光ディスク装置では、図８（Ａ）に示す４Ｔの記録信号（ＥＦＭ信号）を記録する場合、図８（Ｂ）に示すように、光ビームパワーを記録信号の値０ではイレーズパワーＰｅに対応させ、記録信号の値１ではライトパワーＰｗとリードパワーＰｂとに対応させて交互に変化させている。なお、基準時間幅Ｔは標準速度（１倍速）にて周波数４．３２ＭＨｚの１周期であり、約２３０ｎｓｅｃである。
【０００５】
このため、再生時は光ビームパワーがリードパワーである反射光を検出してトラッキングエラー信号を生成し、記録時には光ビームパワーがイレーズパワーであるタイミングの反射光をサンプルホールドしてトラッキングエラー信号を生成している。
【０００６】
図９及び図１０は、従来のサーボ信号生成回路の一例の回路構成図を示す。図９において、光ディスクに光ビームスポットを照射して、その反射ビーム（戻り光）を４分割した光検出器１０Ａ，１０Ｂ，１０Ｃ，１０Ｄで検出する。光検出器１０Ａ，１０Ｂ，１０Ｃ，１０Ｄそれぞれの検出信号はサンプルホールド回路ＳＡ，ＳＢ，ＳＣ，ＳＤに供給される。サンプルホールド回路ＳＡ，ＳＢ，ＳＣ，ＳＤは端子１２から供給されるサンプルホールド信号が例えばハイレベルのタイミングで検出信号をサンプルホールドして増幅器ＧＡ，ＧＢ，ＧＣ，ＧＤそれぞれに供給する。増幅器ＧＡ，ＧＢ，ＧＣ，ＧＤは端子１４から供給されるゲイン切り換え信号に基づいて、上記検出信号に対するゲインを記録時と再生時とで切り換えることにより、検出信号のレベルを記録時と再生時とで同程度として端子１６Ａ，１６Ｂ，１６Ｃ，１６Ｄそれぞれより出力する。
【０００７】
上記従来のサーボ信号生成回路では、増幅器ＧＡ，ＧＢ，ＧＣ，ＧＤのゲイン切り換えによって生じるオフセット電圧の変化が、そのまま後続のサーボ信号演算部に入力されるため、生成されるサーボ信号の総オフセット電圧に影響を与える。特に和信号の場合、差信号のように演算によるオフセット電圧の打ち消し効果がないため、オフセット電圧の変化分の影響は無視できないほど大きくなる。従って、ゲイン切り換え毎に補正オフセット電圧を切り換える必要がある。
【０００８】
図１０において、増幅器ＧＡ，ＧＢ，ＧＣ，ＧＤの出力する検出信号Ａ，Ｂ，Ｃ，Ｄは演算部１８，２０に供給される。演算部１８は検出信号Ａ，Ｂ，Ｃ，Ｄそれぞれと端子１９よりの和信号用補正オフセット電圧Ｖｏｓａｄｄとを加算して、戻り光量モニタ信号としての和信号（Ａ＋Ｂ＋Ｃ＋Ｄ）を生成して端子２２から出力する。また、演算部２０は検出信号Ａ，Ｂ，Ｃ，Ｄそれぞれと端子２１よりの差信号用補正オフセット電圧Ｖｏｓｓｕｂとを加減算して、サーボ信号としての差信号（Ａ＋Ｂ）−（Ｃ＋Ｄ）を生成して端子２４から出力する。
【０００９】
【発明が解決しようとする課題】
ここで、サンプルホールド回路ＳＡ，ＳＢ，ＳＣ，ＳＤそれぞれが出力する検出信号Ａ，Ｂ，Ｃ，Ｄそれぞれのオフセット電圧値をＶａ，Ｖｂ，Ｖｃ，Ｖｄとし、増幅器ＧＡ，ＧＢ，ＧＣ，ＧＤそれぞれの入力オフセット電圧値をＶｇａ，Ｖｇｂ，Ｖｇｃ，Ｖｇｄとし、増幅器ＧＡ，ＧＢ，ＧＣ，ＧＤそれぞれのゲインをＧとし、演算部１８，２０のオフセット電圧はないものとする。このとき、和信号の総オフセット電圧値Ｖａｄｄは（１）式で表される。
【００１０】
Ｖａｄｄ＝Ｇ（Ｖａ＋Ｖｂ＋Ｖｃ＋Ｖｄ＋Ｖｇａ＋Ｖｇｂ＋Ｖｇｃ＋Ｖｇｄ）…（１）
つまり、和信号用補正オフセット電圧Ｖｏｓａｄｄを−Ｖａｄｄと同一にすれば、和信号の総オフセット電圧値Ｖａｄｄを補償することができるから、
Ｖｏｓａｄｄ＝−Ｇ（Ｖａ＋Ｖｂ＋Ｖｃ＋Ｖｄ＋Ｖｇａ＋Ｖｇｂ＋Ｖｇｃ＋Ｖｇｄ）
しかし、上式で表される和信号用補正オフセット電圧ＶｏｓａｄｄにはゲインＧが入っているため、和信号用補正オフセット電圧ＶｏｓａｄｄはゲインＧの切り換えに従って値を変更しなければならないという問題があった。
【００１１】
また、差信号の総オフセット電圧値Ｖｓｕｂは（２）式で表される。
【００１２】

Figure 0003622650
つまり、差信号用補正オフセット電圧Ｖｏｓｓｕｂを−Ｖｓｕｂと同一にすれば、差信号の総オフセット電圧値Ｖｓｕｂを補償することができるから、
Ｖｏｓｓｕｂ＝−Ｇ［（Ｖａ＋Ｖｂ＋Ｖｇａ＋Ｖｇｂ）−（Ｖｃ＋Ｖｄ＋Ｖｇｃ＋Ｖｇｄ）］
しかし、上式で表される差信号用補正オフセット電圧ＶｏｓｓｕｂにはゲインＧが入っているため、差信号用補正オフセット電圧はゲインＧの切り換えに従って値を変更しなければならないという問題があった。
【００１３】
本発明は、上記の点に鑑みなされたもので、増幅器のゲイン切り換えに拘わらず補正オフセット電圧値を変更する必要のない光ディスク装置を提供することを目的とする。
【００１４】
【課題を解決するための手段】
請求項１に記載の発明は、光ディスクに照射する光ビームの強度を記録時と再生時とで変化させる光ディスク装置において、
光ディスクに照射した光ビームの反射光を検出する複数に分割された第１、第２、第３、第４の光検出器と、
前記第１、第２、第３、第４の光検出器の出力信号を記録時と再生時とでゲインを変化させてそれぞれ増幅する第１、第２、第３、第４の増幅器と、
前記第１、第２、第３、第４の増幅器の出力信号を加算して和信号を得る第１の演算器と、
前記第１、第２の増幅器の出力信号を加算するとともに、第３、第４の増幅器の出力信号を減算して差信号を得る第２の演算器とを有し、
前記第１、第２、第３、第４の光検出器及び増幅器のオフセットによる前記和信号の総オフセットを補正する信号を増幅器の数及びゲインで除算した和信号用補正オフセット信号が前記第１、第２、第３、第４の増幅器に加算入力され、
前記第１、第２、第３、第４の光検出器及び増幅器のオフセットによる前記差信号の総オフセットを補正する信号を増幅器の数及びゲインで除算した差信号用補正オフセット信号が前記第１、第２の増幅器に加算入力され、前記第３、第４の増幅器に減算入力されることにより、第１の演算器及び第２の演算器の演算結果からオフセットを除去することができる。
【００１６】
請求項２に記載の発明は、光ディスクに照射する光ビームの強度を記録時と再生時とで変化させる光ディスク装置において、
光ディスクに照射した光ビームの反射光を検出する複数に分割された第１、第２、第３、第４の光検出器と、
前記第１、第２、第３、第４の光検出器の出力信号を記録時と再生時とでゲインを変化させてそれぞれ増幅する第１、第２、第３、第４の増幅器と、
前記第１、第２、第３、第４の増幅器の出力信号を加算して和信号を得る第１の演算器と、
前記第１、第４の増幅器の出力信号を加算するとともに、第２、第３の増幅器の出力信号を減算して差信号を得る第２の演算器と、
前記第１、第２の増幅器の出力信号を加算するとともに、第３、第４の増幅器の出力信号を減算して差信号を得る第３の演算器とを有し、
前記第１、第２、第３、第４の光検出器及び増幅器のオフセットによる前記和信号の総オフセットを補正する信号を前記ゲインで除算するとともに２等分した前記第１の演算器用の和信号補正オフセット信号が第１及び第３の増幅器に加算入力され、
前記第１、第２、第３、第４の光検出器及び増幅器のオフセットによる前記差信号の総オフセットを補正する信号を前記ゲインで除算するとともに２等分した前記第２の演算器用の差信号補正オフセット信号が前記第３の増幅器に減算入力され、前記第４の増幅器に加算入力され、
前記第１、第２、第３、第４の光検出器及び増幅器のオフセットによる前記差信号の総オフセットを補正する信号を前記ゲインで除算するとともに２等分した前記第３の演算器用の差信号補正オフセット信号が前記第１の増幅器に加算入力され、前記第４の増幅器に減算入力されることにより、第１、第２、第３の演算器の演算結果からオフセットを除去できる。
【００１７】
【発明の実施の形態】
図１は、本発明の光ディスク装置の一実施例のブロック図を示す。同図中、ＣＤ−ＲやＣＤ−ＲＷ等の記録型光ディスク４０は図示しないスピンドルモータにより所定の回転速度で回転駆動される。光ピックアップ４２は図示しないスレッドモータによりディスク半径方向に移動せしめられる。光ピックアップ４２は光学系対物レンズ、アクチュエータ、１／４波長板、コリメータレンズ、ビームスプリッタ、発光素子（レーザダイオード）及びフロントモニタ、光検出器等から構成されている。
【００１８】
ＬＤ制御回路４４は再生時にはリードパワーで、また、記録時には記録パルスに基づき、イレーズパワーＰｅ，ライトパワーＰｗ，リードパワーＰｂで、光ピックアップ４２内のレーザダイオードを発光させ、レーザビーム（光ビーム）を出力させる。また、ＬＤ制御回路４４は光ピックアップ４２内のフロントモニタで検出されたレーザビームの光強度に基づいてレーザビームのパワーが最適となるようにレーザドライバを制御する。
【００１９】
ＲＦアンプ４６は光ピックアップ４２内の光検出器により光ディスクから再生された再生信号を増幅するヘッドアンプである。このＲＦアンブ４６で増幅された再生信号は、信号再生処理回路４８に供給されると共に、サーボ信号生成回路５０に供給される。
【００２０】
信号再生処理回路４８はＣＩＲＣ（Ｃｒｏｓｓ Ｉｎｔｅｒｌｅａｖｅｄ Ｒｅａｄ−ｓｏｌｏｍｏｎ Ｃｏｄｅ）のデコード、及びＥＦＭ（Ｅｉｇｈｔ ｔｏ Ｆｏｕｒｔｅｅｎ Ｍｏｄｕｌａｔｉｏｎ）復調、及び同期検出等の処理を行い、更に、ＣＤ−ＲＯＭ固有のＥＣＣ（Ｅｒｒｏｒ Ｃｏｒｒｅｃｔ Ｃｏｄｅ）のデコード、及びヘッダの検出等の処理を行って、再生データを図示しない後段回路に供給する。
【００２１】
端子５３より入来する記録パルスは、ＬＤ制御回路４４に供給されると共に、サンプリングパルス生成回路５２に供給される。サンプリングパルス生成回路５２は記録パルスに基づいてサンプルホールド信号を生成し、サーボ信号生成回路５０に供給する。オフセット付与回路５４には、和信号用補正オフセット電圧及び差信号用補正オフセット電圧が予め保持されており、この和信号用補正オフセット電圧及び差信号用補正オフセット電圧がサーボ信号生成回路５０に供給される。
【００２２】
サーボ信号生成回路５０は、サンプリングパルス生成回路５２からのサンプルホールド信号に従って光検出器の検出信号をサンプルホールドし、オフセット付与回路５４からの和信号用補正オフセット電圧及び差信号用補正オフセット電圧を加算して、戻り光量モニタ信号としての和信号とサーボ信号としての差信号とを生成する。この差信号と和信号はサーボ回路５６に供給され、サーボ回路５６は光ピックアップ４２内のアクチュエータを駆動してトラッキングサーボ及びフォーカスサーボの制御を行う。
【００２３】
図２は、本発明のサーボ信号生成回路の第１実施例の回路構成図を示す。図２において、光ディスクに光ビームスポットを照射して、その反射ビーム（戻り光）を４分割した光検出器６０Ａ，６０Ｂ，６０Ｃ，６０Ｄで検出する。光検出器６０Ａ，６０Ｂ，６０Ｃ，６０Ｄそれぞれの検出信号はサンプルホールド回路ＳＡ，ＳＢ，ＳＣ，ＳＤに供給される。
【００２４】
サンプルホールド回路ＳＡ，ＳＢ，ＳＣ，ＳＤそれぞれはスイッチとコンデンサとから構成されており、端子６２から供給されるサンプルホールド信号が例えばハイレベルのタイミングでスイッチをオンして検出信号をサンプリングしてコンデンサにホールドし、増幅器６６Ａ，６６Ｂ，６６Ｃ，６６Ｄそれぞれに供給する。
【００２５】
増幅器６６Ａ，６６Ｂ，６６Ｃ，６６Ｄは端子６４から供給されるゲイン切り換え信号に基づいて上記検出信号に対するゲインを記録時と再生時とで切り換えて検出信号のレベルを記録時と再生時とで同程度とする。また、増幅器６６Ａ，６６Ｂは上記検出信号に端子６８から供給される和信号用補正オフセット電圧Ｖｏｓａｄｄと端子７０から供給される差信号用補正オフセット電圧Ｖｏｓｓｕｂとを加算しており、増幅器６６Ｃ，６６Ｄは上記検出信号に和信号用補正オフセット電圧Ｖｏｓａｄｄを加算し、差信号用補正オフセット電圧Ｖｏｓｓｕｂを減算している。
【００２６】
増幅器６６Ａ，６６Ｂ，６６Ｃ，６６Ｄの出力する検出信号Ａ，Ｂ，Ｃ，Ｄは演算部７２，７６に供給される。演算部７２は検出信号Ａ，Ｂ，Ｃ，Ｄそれぞれを加算して、戻り光量モニタ信号としての和信号（Ａ＋Ｂ＋Ｃ＋Ｄ）を生成して端子７４から出力する。また、演算部７６は検出信号Ａ，Ｂを加算し検出信号Ｃ，Ｄを減算して、トラッキングサーボ信号としての差信号（Ａ＋Ｂ）−（Ｃ＋Ｄ）を生成して端子７８から出力する。
【００２７】
ここで、図２から一部回路を抜粋した図３を用いて、和信号（Ａ＋Ｂ＋Ｃ＋Ｄ）における和信号用補正オフセット電圧Ｖｏｓａｄｄについて考える。
【００２８】
サンプルホールド回路ＳＡ，ＳＢ，ＳＣ，ＳＤそれぞれが出力する検出信号Ａ，Ｂ，Ｃ，Ｄそれぞれのオフセット電圧値をＶａ，Ｖｂ，Ｖｃ，Ｖｄとし、増幅器６６Ａ，６６Ｂ，６６Ｃ，６６Ｄそれぞれの入力オフセット電圧値をＶｇａ，Ｖｇｂ，Ｖｇｃ，Ｖｇｄとし、増幅器６６Ａ，６６Ｂ，６６Ｃ，６６ＤそれぞれのゲインをＧとし、演算部７２，７６のオフセット電圧はないものとする。このとき、和信号の総オフセット電圧値Ｖａｄｄは（３）式で表される。
【００２９】
Ｖａｄｄ＝Ｇ（Ｖａ＋Ｖｂ＋Ｖｃ＋Ｖｄ＋Ｖｇａ＋Ｖｇｂ＋Ｖｇｃ＋Ｖｇｄ）…（３）
従って、４ＧＶｏｓａｄｄ＝−Ｖａｄｄとすれば、和信号の総オフセット電圧値Ｖａｄｄを補償することができるから、
Figure 0003622650
この場合、和信号用補正オフセット電圧Ｖｏｓａｄｄには、ゲインＧが存在しないため、ゲインＧの切り替えの影響を受けることがない。
【００３０】
次に、図２から一部回路を抜粋した図４を用いて、差信号（Ａ＋Ｂ）−（Ｃ＋Ｄ）における和信号用補正オフセット電圧Ｖｏｓａｄｄの影響について考える。差信号の総オフセット電圧値Ｖｓｕｂは（５）式で表される。
【００３１】
Figure 0003622650
つまり、和信号用補正オフセット電圧Ｖｏｓａｄｄは差信号の総オフセット電圧値Ｖｓｕｂに影響を与えないことが判る。
【００３２】
次に、図２から一部回路を抜粋した図５を用いて、差信号（Ａ＋Ｂ）−（Ｃ＋Ｄ）における差信号用補正オフセット電圧Ｖｏｓｓｕｂについて考える。
差信号の総オフセット電圧値Ｖｓｕｂは前出の（５）式で表される。従って、４ＧＶｏｓｓｕｂ＝−Ｖｓｕｂとすれば、差信号の総オフセット電圧値Ｖｓｕｂを補償することができるから、
Figure 0003622650
この場合、差信号用補正オフセット電圧Ｖｏｓｓｕｂには、ゲインＧが存在しないため、ゲインＧの切り替えの影響を受けることがない。
【００３３】
次に、図２から一部回路を抜粋した図６を用いて、和信号（Ａ＋Ｂ＋Ｃ＋Ｄ）における差信号用補正オフセット電圧Ｖｏｓｓｕｂの影響について考える。和信号の総オフセット電圧値Ｖａｄｄは（７）式で表される。
【００３４】
Figure 0003622650
つまり、（３）式と同一となり、差信号用補正オフセット電圧Ｖｏｓｓｕｂは和信号の総オフセット電圧値Ｖａｄｄに影響を与えないことが判る。
【００３５】
図７は、本発明のサーボ信号生成回路の第２実施例の回路構成図を示す。同図中、図２と同一部分には同一符合を付す。図７において、光ディスクに光ビームスポットを照射して、その反射ビーム（戻り光）を４分割した光検出器６０Ａ，６０Ｂ，６０Ｃ，６０Ｄで検出する。光検出器６０Ａ，６０Ｂ，６０Ｃ，６０Ｄそれぞれの検出信号はサンプルホールド回路ＳＡ，ＳＢ，ＳＣ，ＳＤに供給される。
【００３６】
サンプルホールド回路ＳＡ，ＳＢ，ＳＣ，ＳＤそれぞれはスイッチとコンデンサとから構成されており、端子６２から供給されるサンプルホールド信号が例えばハイレベルのタイミングでスイッチをオンして検出信号をサンプリングしてコンデンサにホールドし、増幅器８０Ａ，８０Ｂ，８０Ｃ，８０Ｄそれぞれに供給する。
【００３７】
増幅器８０Ａ，８０Ｂ，８０Ｃ，８０Ｄは端子６４から供給されるゲイン切り換え信号に基づいて上記検出信号に対するゲインを記録時と再生時とで切り換えて検出信号のレベルを記録時と再生時とで同程度とする。また、増幅器８０Ａは上記検出信号に端子６８から供給される和信号用補正オフセット電圧Ｖｏｓａｄｄと端子８４から供給されるトラッキングエラー信号用補正オフセット電圧Ｖｏｓｔｅとを加算している。増幅器８０Ｃは上記検出信号に和信号用補正オフセット電圧Ｖｏｓａｄｄを加算し、端子８２から供給されるフォーカスエラー信号用補正オフセット電圧Ｖｏｓｆｅを減算している。
【００３８】
また、増幅器８０Ｄは上記検出信号にフォーカスエラー信号用補正オフセット電圧Ｖｏｓｆｅを加算し、トラッキングエラー信号用補正オフセット電圧Ｖｏｓｔｅを減算している。増幅器８０Ｂにはオフセット電圧は供給されない。増幅器８０Ａ，８０Ｂ，８０Ｃ，８０Ｄの出力する検出信号Ａ，Ｂ，Ｃ，Ｄは演算部８６，８８，９０それぞれに供給される。
【００３９】
演算部８６は検出信号Ａ，Ｂ，Ｃ，Ｄそれぞれを加算して、戻り光量モニタ信号としての和信号（Ａ＋Ｂ＋Ｃ＋Ｄ）を生成して端子８７から出力する。また、演算部８８は検出信号Ａ，Ｄを加算し検出信号Ｂ，Ｃを減算して、フォーカスサーボ信号としての差信号（Ａ＋Ｄ）−（Ｂ＋Ｃ）を生成して端子８９から出力する。また、演算部９０は検出信号Ａ，Ｂ，を加算し検出信号Ｃ，Ｄを減算して、トラッキングサーボ信号（Ａ＋Ｂ）−（Ｃ＋Ｄ）を生成して端子９１から出力する。
【００４０】
ここで、和信号の総オフセット電圧をＶａｄｄ、和信号用補正オフセット電圧をＶｏｓａｄｄ、フォーカスサーボ信号の総オフセット電圧をＶｆｅ、フォーカスサーボ信号用補正オフセット電圧をＶｏｓｆｅ、トラッキングサーボ信号の総オフセット電圧をＶｔｅ、トラッキングサーボ信号用補正オフセット電圧をＶｏｓｔｅ、サンプルホールド回路ＳＡ，ＳＢ，ＳＣ，ＳＤそれぞれが出力する検出信号Ａ，Ｂ，Ｃ，Ｄそれぞれのオフセット電圧値をＶａ，Ｖｂ，Ｖｃ，Ｖｄとし、増幅器８０Ａ，８０Ｂ，８０Ｃ，８０Ｄそれぞれの入力オフセット電圧値をＶｇａ，Ｖｇｂ，Ｖｇｃ，Ｖｇｄとし、増幅器８０Ａ，８０Ｂ，８０Ｃ，８０ＤそれぞれのゲインをＧとし、演算部８６，８８，９０のオフセット電圧はないものとすると、下記の関係になる。
【００４１】
Figure 0003622650
従って、２ＧＶｏｓａｄｄ＝−Ｖａｄｄとすれば、和信号の総オフセット電圧値Ｖａｄｄを補償することができ、また、
Ｖａｄｄ＝Ｇ（Ｖａ＋Ｖｂ＋Ｖｃ＋Ｖｄ＋Ｖｇａ＋Ｖｇｂ＋Ｖｇｃ＋Ｖｇｄ）であるから、
Figure 0003622650
となり、和信号用補正オフセット電圧Ｖｏｓａｄｄには、ゲインＧが存在しないため、ゲインＧの切り替えの影響を受けることがない。また、
Figure 0003622650
従って、２ＧＶｏｓｆｅ＝−Ｖｆｅとすれば、フォーカスサーボ信号の総オフセット電圧値Ｖｆｅを補償することができ、また、
Ｖｆｅ＝Ｇ（Ｖａ−Ｖｂ−Ｖｃ＋Ｖｄ＋Ｖｇａ−Ｖｇｂ−Ｖｇｃ＋Ｖｇｄ）であるから、
Figure 0003622650
となり、フォーカスサーボ信号用補正オフセット電圧Ｖｏｓｆｅには、ゲインＧが存在しないため、ゲインＧの切り替えの影響を受けることがない。また、
Figure 0003622650
従って、２ＧＶｏｓｔｅ＝−Ｖｔｅとすれば、トラッキングサーボ信号の総オフセット電圧値Ｖｔｅを補償することができ、また、
Ｖｔｅ＝Ｇ（Ｖａ＋Ｖｂ−Ｖｃ−Ｖｄ＋Ｖｇａ＋Ｖｇｂ−Ｖｇｃ−Ｖｇｄ）であるから、
Figure 0003622650
となり、トラッキングサーボ信号用補正オフセット電圧Ｖｏｓｔｅには、ゲインＧが存在しないため、ゲインＧの切り替えの影響を受けることがない。
【００４２】
このように、目的の演算にのみ作用し、他の演算ではキャンセルされるように補正オフセット電圧を印可することにより、様々な演算の組み合わせに応用することができる。
【００４３】
なお、演算器７２が請求項記載の第１の演算器に対応し、演算器７６が第２の演算器に対応し、和信号用補正オフセット電圧Ｖｏｓａｄｄが第１の補正オフセット値に対応し、差信号用補正オフセット電圧Ｖｏｓｓｕｂが第２の補正オフセット値に対応する。
【００４４】
【発明の効果】
上述の如く、請求項１に記載の発明によれば、第１の演算器及び第２の演算器の演算結果からオフセットを除去することができる。
【００４６】
請求項２に記載の発明によれば、第１、第２、第３の演算器の演算結果からオフセットを除去できる。
【図面の簡単な説明】
【図１】本発明の光ディスク装置の一実施例のブロック図である。
【図２】本発明のサーボ信号生成回路の第１実施例の回路構成図である。
【図３】図２から一部回路を抜粋した回路構成図である。
【図４】図２から一部回路を抜粋した回路構成図である。
【図５】図２から一部回路を抜粋した回路構成図である。
【図６】図２から一部回路を抜粋した回路構成図である。
【図７】本発明のサーボ信号生成回路の第２実施例の回路構成図である。
【図８】書き換え可能型光ディスクの記録信号と光ビームパワーを説明するための波形図である。
【図９】従来のサーボ信号生成回路の一例の回路構成図である。
【図１０】従来のサーボ信号生成回路の一例の回路構成図である。
【符号の説明】
４０ 記録型光ディスク
４２ 光ピックアップ
４４ ＬＤ制御回路
４６ ＲＦアンプ
４８ 信号再生処理回路
５０ サーボ信号生成回路
５２ サンプリングパルス生成回路
５４ オフセット付与回路
５６ サーボ回路
６０Ａ，６０Ｂ，６０Ｃ，６０Ｄ 光検出器
ＳＡ，ＳＢ，ＳＣ，ＳＤ サンプルホールド回路
６６Ａ，６６Ｂ，６６Ｃ，６６Ｄ 増幅器
７２，７６ 演算部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an optical disc apparatus, and more particularly to an optical disc apparatus that records data on a rewritable optical disc.
[0002]
[Prior art]
The recordable optical disc includes a write once type and a rewritable type. Pre-grooves (grooves) for guides are used for CD-R (Compact Disk Rerecordable), which is a write once optical disk, CD-RW (Compact Disk Rewriteable), or DVD-RW (Digital Versatile Disk Rewriteable), which is a rewritable optical disk. Is provided. For example, the pregroove is wobbled in a slight radial direction at a center frequency of 22.05 kHz, and address information during recording called ATIP (Absolute Time In Pregroove) is multiplexed by FSK modulation with a maximum deviation of ± 1 kHz. Are recorded.
[0003]
The tracking and focus servo circuit of an optical disk apparatus that performs recording and reproduction of such a recordable optical disk irradiates the optical disk with a light beam, detects reflected light from the optical disk with a plurality of photodetectors, and uses this detection signal. A servo signal is generated by performing a predetermined calculation, and an actuator is driven based on the servo signal to perform tracking and focus servo.
[0004]
Here, in an optical disc apparatus that performs recording / reproduction such as CD-RW, which is a rewritable optical disc, when recording a 4T recording signal (EFM signal) shown in FIG. 8A, as shown in FIG. 8B. In addition, the light beam power is changed in correspondence with the erase power Pe when the value of the recording signal is 0, and is changed alternately according to the write power Pw and the read power Pb when the value of the recording signal is 1. The reference time width T is one cycle of a frequency of 4.32 MHz at a standard speed (1 × speed), and is about 230 nsec.
[0005]
Therefore, during playback, the reflected light whose light beam power is the read power is detected and a tracking error signal is generated, and during recording, the reflected light at the timing when the light beam power is the erase power is sampled and held to generate the tracking error signal. Is generated.
[0006]
9 and 10 show circuit configuration diagrams of an example of a conventional servo signal generation circuit. In FIG. 9, an optical disk is irradiated with a light beam spot, and the reflected beam (return light) is detected by photodetectors 10A, 10B, 10C, and 10D divided into four. The detection signals of the photodetectors 10A, 10B, 10C, and 10D are supplied to sample and hold circuits SA, SB, SC, and SD. The sample and hold circuits SA, SB, SC, and SD sample and hold the detection signal when the sample and hold signal supplied from the terminal 12 is at a high level, for example, and supply it to the amplifiers GA, GB, GC, and GD, respectively. The amplifiers GA, GB, GC, and GD switch the gain for the detection signal between recording and reproduction based on the gain switching signal supplied from the terminal 14, thereby changing the level of the detection signal between recording and reproduction. Are output from the terminals 16A, 16B, 16C, and 16D as the same degree.
[0007]
In the conventional servo signal generation circuit, the change in offset voltage caused by the gain switching of the amplifiers GA, GB, GC, and GD is directly input to the subsequent servo signal calculation unit. To affect. In particular, in the case of a sum signal, there is no effect of canceling the offset voltage by calculation as in the case of the difference signal, so the influence of the change in the offset voltage becomes so large that it cannot be ignored. Therefore, it is necessary to switch the correction offset voltage every time the gain is switched.
[0008]
In FIG. 10, detection signals A, B, C, and D output from amplifiers GA, GB, GC, and GD are supplied to arithmetic units 18 and 20, respectively. The calculation unit 18 adds each of the detection signals A, B, C, and D and the correction offset voltage Vosadd for the sum signal from the terminal 19 to generate a sum signal (A + B + C + D) as a return light amount monitor signal from the terminal 22. Output. The arithmetic unit 20 adds and subtracts each of the detection signals A, B, C, and D and the difference signal correction offset voltage Vossub from the terminal 21 to generate a difference signal (A + B) − (C + D) as a servo signal. Output from the terminal 24.
[0009]
[Problems to be solved by the invention]
Here, the offset voltage values of the detection signals A, B, C, and D output from the sample hold circuits SA, SB, SC, and SD are Va, Vb, Vc, and Vd, respectively, and the amplifiers GA, GB, GC, and GD, respectively. Are assumed to be Vga, Vgb, Vgc, Vgd, G is the gain of each of the amplifiers GA, GB, GC, GD, and there is no offset voltage of the arithmetic units 18, 20. At this time, the total offset voltage value Vadd of the sum signal is expressed by equation (1).
[0010]
Vadd = G (Va + Vb + Vc + Vd + Vga + Vgb + Vgc + Vgd) (1)
That is, if the sum signal correction offset voltage Vosadd is made equal to −Vadd, the total offset voltage value Vadd of the sum signal can be compensated.
Vosadd = −G (Va + Vb + Vc + Vd + Vga + Vgb + Vgc + Vgd)
However, since the sum signal correction offset voltage Vosadd represented by the above formula includes the gain G, the sum signal correction offset voltage Vosadd has to be changed in accordance with the switching of the gain G. .
[0011]
Further, the total offset voltage value Vsub of the difference signal is expressed by equation (2).
[0012]
Figure 0003622650
In other words, if the difference signal correction offset voltage Vossub is made equal to -Vsub, the total offset voltage value Vsub of the difference signal can be compensated.
Vossub = −G [(Va + Vb + Vga + Vgb) − (Vc + Vd + Vgc + Vgd)]
However, since the gain G is included in the difference signal correction offset voltage Vossub represented by the above equation, there is a problem that the value of the difference signal correction offset voltage must be changed according to the switching of the gain G.
[0013]
The present invention has been made in view of the above points, and an object of the present invention is to provide an optical disc apparatus that does not require a correction offset voltage value to be changed regardless of gain switching of an amplifier.
[0014]
[Means for Solving the Problems]
The invention according to claim 1 is an optical disc apparatus in which the intensity of a light beam applied to an optical disc is changed between recording and reproduction.
A plurality of first, second, third, and fourth photodetectors that detect a reflected light of a light beam applied to the optical disc;
Said first, second, third, first for amplifying respectively by changing the gain at the time of recording the output signal of the fourth photodetector and the time of reproduction, second, third, and fourth amplifier,
A first computing unit that adds the output signals of the first, second, third, and fourth amplifiers to obtain a sum signal;
A second computing unit that adds the output signals of the first and second amplifiers and subtracts the output signals of the third and fourth amplifiers to obtain a difference signal;
The correction offset signal for the sum signal obtained by dividing the signal for correcting the total offset of the sum signal by the offsets of the first, second, third, and fourth photodetectors and the amplifier by the number of amplifiers and the gain is the first signal. , Added to the second, third and fourth amplifiers,
A difference signal correction offset signal obtained by dividing a signal for correcting the total offset of the difference signal by the offsets of the first, second, third, and fourth photodetectors and the amplifier by the number of amplifiers and the gain is the first offset signal. The addition is input to the second amplifier and the subtraction is input to the third and fourth amplifiers, so that the offset can be removed from the calculation results of the first calculator and the second calculator.
[0016]
The invention according to claim 2 is an optical disc apparatus in which the intensity of the light beam applied to the optical disc is changed between recording and reproduction.
A plurality of first, second, third, and fourth photodetectors that detect a reflected light of a light beam applied to the optical disc;
First, second, third, and fourth amplifiers that amplify the output signals of the first, second, third, and fourth photodetectors by changing gains during recording and reproduction, respectively;
A first computing unit that adds the output signals of the first, second, third, and fourth amplifiers to obtain a sum signal;
A second arithmetic unit that adds the output signals of the first and fourth amplifiers and subtracts the output signals of the second and third amplifiers to obtain a difference signal;
A third arithmetic unit that adds the output signals of the first and second amplifiers and subtracts the output signals of the third and fourth amplifiers to obtain a difference signal;
The sum for the first arithmetic unit is obtained by dividing the signal for correcting the total offset of the sum signal due to the offsets of the first, second, third, and fourth photodetectors and the amplifier by the gain and dividing the signal into two equal parts. A signal correction offset signal is added and input to the first and third amplifiers,
The difference for the second arithmetic unit is obtained by dividing the signal for correcting the total offset of the difference signal due to the offsets of the first, second, third, and fourth photodetectors and the amplifier by the gain and dividing the signal into two equal parts. A signal correction offset signal is subtracted and input to the third amplifier and added to the fourth amplifier.
The signal for correcting the total offset of the difference signal due to the offset of the first, second, third, and fourth photodetectors and the amplifier is divided by the gain and divided into two equal parts, and the difference for the third arithmetic unit By adding the signal correction offset signal to the first amplifier and subtracting it to the fourth amplifier, the offset can be removed from the calculation results of the first, second, and third calculators .
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram showing an embodiment of an optical disc apparatus according to the present invention. In the figure, a recordable optical disk 40 such as a CD-R or CD-RW is rotationally driven at a predetermined rotational speed by a spindle motor (not shown). The optical pickup 42 is moved in the disk radial direction by a thread motor (not shown). The optical pickup 42 includes an optical system objective lens, an actuator, a quarter wavelength plate, a collimator lens, a beam splitter, a light emitting element (laser diode), a front monitor, a photodetector, and the like.
[0018]
The LD control circuit 44 causes the laser diode in the optical pickup 42 to emit light at the read power at the time of reproduction and at the erase power Pe, the write power Pw, and the read power Pb based on the recording pulse at the time of recording, and a laser beam (light beam). Is output. The LD control circuit 44 controls the laser driver so that the power of the laser beam is optimized based on the light intensity of the laser beam detected by the front monitor in the optical pickup 42.
[0019]
The RF amplifier 46 is a head amplifier that amplifies a reproduction signal reproduced from the optical disk by a photodetector in the optical pickup 42. The reproduction signal amplified by the RF amplifier 46 is supplied to the signal reproduction processing circuit 48 and also to the servo signal generation circuit 50.
[0020]
The signal reproduction processing circuit 48 performs processing such as CIRC (Cross Interleaved Read-Solomon Code) decoding, EFM (Eight to Fourteen Modulation) demodulation and synchronization detection, and further, a CD-ROM-specific ECC (Error Correct Code). The reproduction data is supplied to a subsequent circuit (not shown).
[0021]
The recording pulse coming from the terminal 53 is supplied to the LD control circuit 44 and also to the sampling pulse generation circuit 52. The sampling pulse generation circuit 52 generates a sample hold signal based on the recording pulse and supplies it to the servo signal generation circuit 50. The offset applying circuit 54 holds a correction offset voltage for sum signal and a correction offset voltage for difference signal in advance, and the correction offset voltage for sum signal and the correction offset voltage for difference signal are supplied to the servo signal generation circuit 50. The
[0022]
The servo signal generation circuit 50 samples and holds the detection signal of the photodetector in accordance with the sample hold signal from the sampling pulse generation circuit 52, and adds the correction offset voltage for the sum signal and the correction offset voltage for the difference signal from the offset applying circuit 54. Then, a sum signal as a return light quantity monitor signal and a difference signal as a servo signal are generated. The difference signal and the sum signal are supplied to a servo circuit 56. The servo circuit 56 drives an actuator in the optical pickup 42 to control tracking servo and focus servo.
[0023]
FIG. 2 shows a circuit configuration diagram of the first embodiment of the servo signal generation circuit of the present invention. In FIG. 2, the optical disk is irradiated with a light beam spot, and the reflected beam (return light) is detected by photodetectors 60A, 60B, 60C, 60D divided into four. Detection signals from the photodetectors 60A, 60B, 60C, and 60D are supplied to sample and hold circuits SA, SB, SC, and SD.
[0024]
Each of the sample hold circuits SA, SB, SC, SD is composed of a switch and a capacitor, and the sample hold signal supplied from the terminal 62 turns on the switch at a high level timing, for example, and samples the detection signal to provide a capacitor. And are supplied to amplifiers 66A, 66B, 66C and 66D, respectively.
[0025]
The amplifiers 66A, 66B, 66C, 66D switch the gain for the detection signal between recording and reproduction based on the gain switching signal supplied from the terminal 64, and the detection signal level is about the same between recording and reproduction. And The amplifiers 66A and 66B add the sum signal correction offset voltage Vosadd supplied from the terminal 68 and the difference signal correction offset voltage Vosub supplied from the terminal 70 to the detection signal. The amplifiers 66C and 66D The sum signal correction offset voltage Vosadd is added to the detection signal, and the difference signal correction offset voltage Vossub is subtracted.
[0026]
Detection signals A, B, C, and D output from the amplifiers 66A, 66B, 66C, and 66D are supplied to arithmetic units 72 and 76, respectively. The computing unit 72 adds the detection signals A, B, C, and D, generates a sum signal (A + B + C + D) as a return light amount monitor signal, and outputs it from the terminal 74. The arithmetic unit 76 adds the detection signals A and B, subtracts the detection signals C and D, generates a difference signal (A + B) − (C + D) as a tracking servo signal, and outputs it from the terminal 78.
[0027]
Here, the correction offset voltage Vosadd for the sum signal in the sum signal (A + B + C + D) will be considered with reference to FIG. 3, which is a partial circuit extracted from FIG.
[0028]
The offset voltage values of the detection signals A, B, C, and D output from the sample hold circuits SA, SB, SC, and SD are Va, Vb, Vc, and Vd, respectively, and the input offsets of the amplifiers 66A, 66B, 66C, and 66D, respectively. Assume that the voltage values are Vga, Vgb, Vgc, and Vgd, the gains of the amplifiers 66A, 66B, 66C, and 66D are G, and there are no offset voltages of the calculation units 72 and 76. At this time, the total offset voltage value Vadd of the sum signal is expressed by equation (3).
[0029]
Vadd = G (Va + Vb + Vc + Vd + Vga + Vgb + Vgc + Vgd) (3)
Therefore, if 4GVosadd = −Vadd, the total offset voltage value Vadd of the sum signal can be compensated.
Figure 0003622650
In this case, since the gain G does not exist in the sum signal correction offset voltage Vosadd, it is not affected by the switching of the gain G.
[0030]
Next, the influence of the correction offset voltage Vosadd for the sum signal on the difference signal (A + B) − (C + D) will be considered with reference to FIG. 4 which is a partial circuit extracted from FIG. The total offset voltage value Vsub of the difference signal is expressed by equation (5).
[0031]
Figure 0003622650
That is, it can be seen that the sum signal correction offset voltage Vosadd does not affect the total offset voltage value Vsub of the difference signal.
[0032]
Next, the difference signal correction offset voltage Vosub in the difference signal (A + B) − (C + D) will be considered with reference to FIG. 5 which is a partial circuit extracted from FIG.
The total offset voltage value Vsub of the difference signal is expressed by the above equation (5). Therefore, if 4GVossub = −Vsub, the total offset voltage value Vsub of the difference signal can be compensated.
Figure 0003622650
In this case, since the gain G does not exist in the difference signal correction offset voltage Vossub, it is not affected by the switching of the gain G.
[0033]
Next, the effect of the difference signal correction offset voltage Vosub on the sum signal (A + B + C + D) will be considered with reference to FIG. 6, which is a partial circuit extracted from FIG. The total offset voltage value Vadd of the sum signal is expressed by equation (7).
[0034]
Figure 0003622650
That is, it becomes the same as the equation (3), and it can be seen that the difference signal correction offset voltage Vosub does not affect the total offset voltage value Vadd of the sum signal.
[0035]
FIG. 7 shows a circuit configuration diagram of a second embodiment of the servo signal generation circuit of the present invention. In the figure, the same parts as those in FIG. In FIG. 7, the optical disk is irradiated with a light beam spot, and the reflected beam (return light) is detected by photodetectors 60A, 60B, 60C, 60D divided into four. Detection signals from the photodetectors 60A, 60B, 60C, and 60D are supplied to sample and hold circuits SA, SB, SC, and SD.
[0036]
Each of the sample hold circuits SA, SB, SC, SD is composed of a switch and a capacitor, and the sample hold signal supplied from the terminal 62 turns on the switch at a high level timing, for example, and samples the detection signal to provide a capacitor. And are supplied to amplifiers 80A, 80B, 80C and 80D, respectively.
[0037]
The amplifiers 80A, 80B, 80C and 80D switch the gain for the detection signal between recording and reproduction based on the gain switching signal supplied from the terminal 64, and the detection signal level is about the same between recording and reproduction. And The amplifier 80A adds the sum signal correction offset voltage Vosadd supplied from the terminal 68 and the tracking error signal correction offset voltage Voste supplied from the terminal 84 to the detection signal. The amplifier 80C adds the correction offset voltage Vosadd for the sum signal to the detection signal, and subtracts the correction offset voltage Vosfe for the focus error signal supplied from the terminal 82.
[0038]
The amplifier 80D adds the focus error signal correction offset voltage Vosfe to the detection signal, and subtracts the tracking error signal correction offset voltage Voste. The offset voltage is not supplied to the amplifier 80B. Detection signals A, B, C, and D output from the amplifiers 80A, 80B, 80C, and 80D are supplied to the arithmetic units 86, 88, and 90, respectively.
[0039]
The calculation unit 86 adds the detection signals A, B, C, and D, generates a sum signal (A + B + C + D) as a return light amount monitor signal, and outputs it from the terminal 87. The arithmetic unit 88 adds the detection signals A and D and subtracts the detection signals B and C to generate a difference signal (A + D) − (B + C) as a focus servo signal and outputs it from the terminal 89. The arithmetic unit 90 adds the detection signals A and B, subtracts the detection signals C and D, generates a tracking servo signal (A + B) − (C + D), and outputs it from the terminal 91.
[0040]
Here, the total offset voltage of the sum signal is Vadd, the correction offset voltage for the sum signal is Vosadd, the total offset voltage of the focus servo signal is Vfe, the correction offset voltage for the focus servo signal is Vosfe, and the total offset voltage of the tracking servo signal is Vte. The tracking servo signal correction offset voltage is Voste, and the offset voltages of the detection signals A, B, C, and D output from the sample hold circuits SA, SB, SC, and SD are Va, Vb, Vc, and Vd, respectively. The input offset voltage values of 80A, 80B, 80C, and 80D are Vga, Vgb, Vgc, and Vgd, the gains of the amplifiers 80A, 80B, 80C, and 80D are G, and there are no offset voltages of the calculation units 86, 88, and 90. Assuming that It made.
[0041]
Figure 0003622650
Therefore, if 2GVosadd = −Vadd, the total offset voltage value Vadd of the sum signal can be compensated, and
Since Vadd = G (Va + Vb + Vc + Vd + Vga + Vgb + Vgc + Vgd),
Figure 0003622650
Therefore, since the gain G does not exist in the sum signal correction offset voltage Vosadd, it is not affected by the switching of the gain G. Also,
Figure 0003622650
Therefore, if 2GVosfe = −Vfe, the total offset voltage value Vfe of the focus servo signal can be compensated, and
Since Vfe = G (Va−Vb−Vc + Vd + Vga−Vgb−Vgc + Vgd),
Figure 0003622650
Therefore, the focus servo signal correction offset voltage Vosfe does not have the gain G, and thus is not affected by the switching of the gain G. Also,
Figure 0003622650
Therefore, if 2GVoste = −Vte, the total offset voltage value Vte of the tracking servo signal can be compensated,
Since Vte = G (Va + Vb−Vc−Vd + Vga + Vgb−Vgc−Vgd),
Figure 0003622650
Therefore, since the gain G does not exist in the tracking servo signal correction offset voltage Voste, it is not affected by the switching of the gain G.
[0042]
In this way, by applying the correction offset voltage so that it affects only the target calculation and is canceled in other calculations, it can be applied to various combinations of calculations.
[0043]
The calculator 72 corresponds to the first calculator, the calculator 76 corresponds to the second calculator, the sum signal correction offset voltage Vosadd corresponds to the first correction offset value, and The difference signal correction offset voltage Vossub corresponds to the second correction offset value.
[0044]
【The invention's effect】
As described above , according to the first aspect of the present invention , it is possible to remove the offset from the calculation results of the first calculator and the second calculator.
[0046]
According to the second aspect of the invention , the offset can be removed from the calculation results of the first, second, and third calculators .
[Brief description of the drawings]
FIG. 1 is a block diagram of an embodiment of an optical disc apparatus according to the present invention.
FIG. 2 is a circuit configuration diagram of a first embodiment of a servo signal generation circuit according to the present invention;
FIG. 3 is a circuit configuration diagram in which some circuits are extracted from FIG. 2;
4 is a circuit configuration diagram in which a part of the circuit is extracted from FIG. 2;
FIG. 5 is a circuit configuration diagram in which some circuits are extracted from FIG. 2;
6 is a circuit configuration diagram in which some circuits are extracted from FIG. 2;
FIG. 7 is a circuit configuration diagram of a second embodiment of the servo signal generation circuit of the present invention.
FIG. 8 is a waveform diagram for explaining a recording signal and light beam power of a rewritable optical disc.
FIG. 9 is a circuit configuration diagram of an example of a conventional servo signal generation circuit.
FIG. 10 is a circuit configuration diagram of an example of a conventional servo signal generation circuit.
[Explanation of symbols]
40 recordable optical disk 42 optical pickup 44 LD control circuit 46 RF amplifier 48 signal reproduction processing circuit 50 servo signal generation circuit 52 sampling pulse generation circuit 54 offset applying circuit 56 servo circuits 60A, 60B, 60C, 60D photodetectors SA, SB, SC, SD Sample and hold circuits 66A, 66B, 66C, 66D Amplifiers 72, 76 Operation unit

Claims (2)

光ディスクに照射する光ビームの強度を記録時と再生時とで変化させる光ディスク装置において、
光ディスクに照射した光ビームの反射光を検出する複数に分割された第１、第２、第３、第４の光検出器と、
前記第１、第２、第３、第４の光検出器の出力信号を記録時と再生時とでゲインを変化させてそれぞれ増幅する第１、第２、第３、第４の増幅器と、
前記第１、第２、第３、第４の増幅器の出力信号を加算して和信号を得る第１の演算器と、
前記第１、第２の増幅器の出力信号を加算するとともに、第３、第４の増幅器の出力信号を減算して差信号を得る第２の演算器とを有し、
前記第１、第２、第３、第４の光検出器及び増幅器のオフセットによる前記和信号の総オフセットを補正する信号を増幅器の数及びゲインで除算した和信号用補正オフセット信号が前記第１、第２、第３、第４の増幅器に加算入力され、
前記第１、第２、第３、第４の光検出器及び増幅器のオフセットによる前記差信号の総オフセットを補正する信号を増幅器の数及びゲインで除算した差信号用補正オフセット信号が前記第１、第２の増幅器に加算入力され、前記第３、第４の増幅器に減算入力されることを特徴とする光ディスク装置。In an optical disc apparatus that changes the intensity of a light beam applied to an optical disc between recording and reproduction,
A plurality of first, second, third, and fourth photodetectors that detect a reflected light of a light beam applied to the optical disc;
Said first, second, third, first for amplifying respectively by changing the gain at the time of recording the output signal of the fourth photodetector and the time of reproduction, second, third, and fourth amplifier,
A first computing unit that adds the output signals of the first, second, third, and fourth amplifiers to obtain a sum signal;
A second computing unit that adds the output signals of the first and second amplifiers and subtracts the output signals of the third and fourth amplifiers to obtain a difference signal;
The correction offset signal for the sum signal obtained by dividing the signal for correcting the total offset of the sum signal by the offsets of the first, second, third, and fourth photodetectors and the amplifier by the number of amplifiers and the gain is the first signal. , Added to the second, third and fourth amplifiers,
A difference signal correction offset signal obtained by dividing a signal for correcting the total offset of the difference signal by the offsets of the first, second, third, and fourth photodetectors and the amplifier by the number of amplifiers and the gain is the first offset signal. An optical disc apparatus , wherein an addition is input to the second amplifier and a subtraction is input to the third and fourth amplifiers . 光ディスクに照射する光ビームの強度を記録時と再生時とで変化させる光ディスク装置において、
光ディスクに照射した光ビームの反射光を検出する複数に分割された第１、第２、第３、第４の光検出器と、
前記第１、第２、第３、第４の光検出器の出力信号を記録時と再生時とでゲインを変化させてそれぞれ増幅する第１、第２、第３、第４の増幅器と、
前記第１、第２、第３、第４の増幅器の出力信号を加算して和信号を得る第１の演算器と、
前記第１、第４の増幅器の出力信号を加算するとともに、第２、第３の増幅器の出力信号を減算して差信号を得る第２の演算器と、
前記第１、第２の増幅器の出力信号を加算するとともに、第３、第４の増幅器の出力信号を減算して差信号を得る第３の演算器とを有し、
前記第１、第２、第３、第４の光検出器及び増幅器のオフセットによる前記和信号の総オフセットを補正する信号を前記ゲインで除算するとともに２等分した前記第１の演算器用の和信号補正オフセット信号が第１及び第３の増幅器に加算入力され、
前記第１、第２、第３、第４の光検出器及び増幅器のオフセットによる前記差信号の総オフセットを補正する信号を前記ゲインで除算するとともに２等分した前記第２の演算器用の差信号補正オフセット信号が前記第３の増幅器に減算入力され、前記第４の増幅器に加算入力され、
前記第１、第２、第３、第４の光検出器及び増幅器のオフセットによる前記差信号の総オフセットを補正する信号を前記ゲインで除算するとともに２等分した前記第３の演算器用の差信号補正オフセット信号が前記第１の増幅器に加算入力され、前記第４の増幅器に減算入力されることを特徴とする光ディスク装置。 In an optical disc apparatus that changes the intensity of a light beam applied to an optical disc between recording and reproduction,
A plurality of first, second, third, and fourth photodetectors that detect a reflected light of a light beam applied to the optical disc;
First, second, third, and fourth amplifiers that amplify the output signals of the first, second, third, and fourth photodetectors by changing gains during recording and reproduction, respectively;
A first computing unit that adds the output signals of the first, second, third, and fourth amplifiers to obtain a sum signal;
A second arithmetic unit that adds the output signals of the first and fourth amplifiers and subtracts the output signals of the second and third amplifiers to obtain a difference signal;
A third arithmetic unit that adds the output signals of the first and second amplifiers and subtracts the output signals of the third and fourth amplifiers to obtain a difference signal;
The sum for the first arithmetic unit is obtained by dividing the signal for correcting the total offset of the sum signal due to the offsets of the first, second, third, and fourth photodetectors and the amplifier by the gain and dividing the signal into two equal parts. A signal correction offset signal is added and input to the first and third amplifiers,
The difference for the second arithmetic unit is obtained by dividing the signal for correcting the total offset of the difference signal due to the offsets of the first, second, third, and fourth photodetectors and the amplifier by the gain and dividing the signal into two equal parts. A signal correction offset signal is subtracted and input to the third amplifier and added to the fourth amplifier.
The signal for correcting the total offset of the difference signal due to the offset of the first, second, third, and fourth photodetectors and the amplifier is divided by the gain and divided into two equal parts, and the difference for the third arithmetic unit An optical disc apparatus , wherein a signal correction offset signal is added to the first amplifier and subtracted to the fourth amplifier .
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